Shoe toe or heel end stiffener

ABSTRACT

A shoe toe or heel end stiffener consisting of a net, at least some strands of which are of hot melt adhesive material having an activation temperature of between 50° C. and 80° C. Suitable adhesive materials include polycaprolactone and certain polyesters. The stiffeners are of improved stiffness per unit weight, in comparison with previously known stiffeners.

TECHNICAL FIELD

[0001] This invention is concerned with a shoe toe or heel end stiffener and is especially concerned with a heel end stiffener.

[0002] The term “shoe” where used herein is to be understood as denoting outer footwear generally whether ready for wear or in the course of manufacture.

BACKGROUND ART

[0003] Some shoes, for example sports shoes, require relatively lightweight heel end stiffeners (commonly referred to as “counters”). Lightweight counters have been provided by techniques well known to those skilled in the art of making counters, for example by extrusion of a relatively stiff thermoplastics film with fabric laminated to one or both sides and adhesive coated but these are relatively complex to manufacture and it is difficult to provide sufficient strength and stiffness while at a very lightweight.

[0004] It has been proposed to eliminate a separate adhesive layer by utilising a thermoplastics material which is sufficiently stiff to provide stiffening but which is adhesive at shoe making temperatures in combination with bulk fibres so that the stiffening material acts as a hot melt adhesive for incorporating the counter in a shoe. Such a counter is described in our co-pending PCT Patent Application No. GB98/03159 which describes a shoe stiffener in which consolidated melt spun fibres of hot melt adhesive are combined with bulk fibres to provide a fibre reinforced hot melt adhesive shoe stiffener film. However, this material requires the hot melt adhesive and the fibrous reinforcement to be melt spun to achieve a satisfactory blend of bulk fibre and adhesive.

DISCLOSURE OF THE INVENTION

[0005] It is one of the various objects of the present invention to provide an improved shoe toe or heel end stiffener.

[0006] The invention may be considered to provide, in one aspect, a shoe toe or heel end stiffener consisting of a net, at least some strands of which are of hot melt adhesive material having an activation temperature of between 50° C. and 80° C. Conveniently, in a stiffener in accordance with the invention, all of the strands of the net may be of hot melt adhesive.

[0007] Alternatively, a shoe stiffener in accordance with the invention may comprise strands of different polymers, some of the strands comprising an adhesive polymer and others of the strands being of a somewhat stiffer polymer which is not adhesive at an activation temperature of between 50° C. and 80° C. For example the net may be a rectangular net in which the parallel strands extending in one direction are hot melt adhesive strands and the strands at right angles thereto do not have a hot melt activation temperature below 80° C. (although they may be thermoplastic but have a significantly higher melting temperature). Conveniently, a stiffener in accordance with the invention of such a net is so constructed and arranged that when incorporated in a shoe, the hot melt adhesive strands are generally parallel to the shoe sole and the other strands at right angles thereto and also generally at right angles to a shoe sole. If desired, however, the stiffeners may be made with the strands at other orientations.

[0008] Nets suitable for use in making a stiffener in accordance with the invention may be made by an extrusion process in which a molten material is extruded through holes in an extrusion die to provide a multiplicity of strands at a suitable spacing. The process is well known to those skilled in the art and the process is designed so that the strands contact one another while still molten, to create a net. Nets of this general type are commercially available, for example from Conwed Plastics, of 2810 Weeks Avenue S.E. Minneapolis, Minn. 55414, United States of America.

[0009] In another stiffener in accordance with the invention some, at least of the strands, may be bi-component, one component being hot melt adhesive material having an activation between 50° C. and 80° C. and the other component having a hot melt activation temperature above 80° C. The other component may be selected to give desired properties to the stiffener and may be either relatively stiff or somewhat less stiff and more flexible such that if deformed the stiffener returns to its undeformed configuration readily. Bi-component fibres may be made by several different techniques which are known to those skilled in the art. Bi-component strands of a sheath/core configuration (with the sheath being of hot melt adhesive material) are preferred.

[0010] The strands of the net in a stiffener in accordance with the invention may have any suitable cross-section or shape, to provide the desired performance. For example the cross-section of the strands may be flat, circular, H-section, multilobal and may be chosen to provide increased stiffness by increasing thickness, or chosen to decrease the risk of print-through ie the strands showing through the material of the shoe upper which is not acceptable.

[0011] The dimensions of the strands in a shoe stiffener in accordance with the invention are chosen in accordance with the desired performance as are the sizes of the openings in the net. Preferably, the openings in the net in a shoe stiffener in accordance with the invention have an area of between 0.03 square centimetres (cm²) and 0.4 cm², more preferably between 0.06 cm² and 0.2 cm².

[0012] Preferably, a stiffener in accordance with the invention has a weight between 250 and 600 grammes per square meter (gsm), more preferably between 300 and 450 gsm.

[0013] Where it is desired that a stiffener in accordance with the invention remains in net form after applying to a shoe upper, so that the shoe upper remains breathable, the spacing, shape and dimensions of the strands of the net should be selected so that the strands do not coalesce during attachment to the upper.

[0014] Hot melt adhesive materials having an activation temperature of between 50° C. and 80° C. which also have sufficient stiffness and strength to provide a required degree of reinforcement to the heel end portion of a shoe upper may be used in a stiffener in accordance with the invention. Suitable materials include polycaprolactone, certain polyester adhesives for example based on poly(tetramethylene adipate) and certain polyurethane adhesives. Suitable polyester-based materials are available from Bostik Limited, Leicester, England, under the trade name Esterpow or Estergran.

[0015] There is hereinafter described, to illustrate the invention by way of example, a shoe counter embodying the invention. It will be realised that this shoe counter has been selected for description to illustrate the invention by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In the accompanying drawing FIG. 1 is a plan view of the illustrative counter.

MODES FOR CARRYING OUT THE INVENTION

[0017] The illustrative counter 8 is cut from a polycaprolactone net supplied by Conwed Plastics and is intended to be inserted into a counter pocket in the back part of a shoe upper. It is well known to those skilled in the art to provide a counter pocket into which a counter is inserted and secured during manufacture of the shoe.

[0018] The strands of the net from which the counter is cut are generally circular in cross-section and are about 1 mm in diameter. The strands are disposed to provide a net of generally rectangular structure with one set of parallel strands 10 arranged so that they extend generally parallel to a shoe sole when the counter 8 is incorporated into a shoe; the other set of strands 12 will therefore extend generally at right angles to the direction of the shoe sole. The strands 12 are spaced such that there are 27 in a 10 centimeter length and the strands 10 are spaced slightly further apart, there being 20 arranged in a 10 centimeter length, that is at a spacing of about 0.5 cm.

[0019] The area in the openings of the net of the illustrative counter 8 is about 0.11 cm². The weight of the illustrative counter is about 340 gsm.

[0020] After the counter 8 has been introduced into the counter pocket, it is subjected to heat and pressure sufficient to activate the polycaprolactone to an adhesive condition, the assembly being heated to a temperature of about 70° C. to activate polycaprolactone adhesive material. After cooling, the illustrative counter 8 provides high stiffness per unit weight of counter with the additional benefit of being breathable.

[0021] In comparison with film counters of approximately the same weight per unit area, the stiffness is considerably greater in the lengthwise direction (that is the direction in which the strands 12 extend) with the stiffness in the transverse direction (that is the direction in which the strands 12 extend) being about the same. The illustrative counter, in view of the openings in the net, is breathable, in comparison with a film counter where there is a continuous impermeable film preventing passage of moisture vapour. The comfort in wear of the illustrative counter may therefore be somewhat greater.

[0022] It is believed that the bulk of the strands is such as to contribute to the improved stiffness per unit weight of counter, because the strands tend to create a “beam” effect which is not present in a film counter. Table 1 gives an indication of the performance of the illustrative counter 8 in comparison with a stiffening material known in the prior art of a comparable weight per unit area.

[0023] The prior stiffening material with which the comparison is made, is in fact, normally, used as a shoe toe end stiffening material and is supplied by the applicant company under the registered trademark, Tufflex, designation E268. The two materials are of generally the same weight in grams per square metre (gsm). The gauge of the illustrative counter 8 is considerably greater which is believed to contribute to the improved stiffness. In Table 1 Stiffness AL is the stiffness measured in a lengthwise direction, namely in the direction parallel with the direction of the strands 12. Stiffness AX is in the transverse direction, that is in the direction parallel with the strands 10. TABLE 1 Illustrative Prior Art Counter Stiffening material Weight (gsm)  341 +/− 0.5  345 +/− 0.095 Gauge (mm) 1.10 +/− 0.0009 0.41 +/− 0.0002 Karl Frank Stiffness AL 62.5 +/− 1.8 21.3 +/− 0.6 AX 16.3 +/− 0.1 18.8 +/− 0.1

[0024] The illustrative counter 8 is not only of increased stiffness per unit weight in comparison with the prior art materials but is also of much simpler structure, being self adhesive as well as the polycaprolactone net providing stiffness without any additional fibre incorporation. 

1. A shoe toe or heel end stiffener consisting of a net, at least some strands of which are of hot melt adhesive material having an activation temperature of between 50° C. and 80° C.
 2. A stiffener according to claim 1 wherein all of the strands of the net are of hot melt adhesive.
 3. A stiffener according to claim 1 wherein the net is a rectangular net in which, when incorporated in a shoe, the hot melt adhesive strands are generally parallel to the shoe sole and the strands at right angles thereto do not have a hot melt activation temperature below 80° C.
 4. A stiffener according to claim 1 where some, at least, of the strands are bi-component, one component being hot melt adhesive material having an activation temperature between 50° C. and 80° C. and the other component having a hot melt activation temperature above 80° C.
 5. A stiffener according to any of claims 1-4, wherein the openings in the net have an area between 0.03 square cm and 0.4 square cm.
 6. A stiffener according to any of claims 1-4, wherein the openings in the net have an area between 0.06 square cm and 0.2 square cm.
 7. A stiffener according to any of claims 1-4 having a weight between 250 and 600 g per square metre.
 8. A stiffener according to claim 7 having a weight between 300 and 450 g per square metre.
 9. A stiffener according to any one of claims 1-4, wherein the hot melt adhesive material comprises polycaprolactone. 